1	Acid Rain Broad term used to describe several ways that acids fall out of the atmosphere
2	Wet and Dry Acid Rain Wet deposition refers to acidic rain, fog, and snow. Dry deposition refers to acidic gases and particles.
3	“Wet” Acid Rain Acidic water flows over and through the ground, it affects a variety of plants and animals.
4	“Dry” Acid Rain Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees.
5	Increased Acidity Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. The runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone.
6	Causes of Acid Rain Sulfur dioxide (SO₂) and nitrogen oxides (NO_x) are the primary causes of acid rain. In the US, About 2/3 of all SO₂ and 1/4 of all NO_x comes from electric power generation that relies on burning fossil fuels like coal.
7	Formation of Acid Rain Gases react in the atmosphere with water, oxygen, and other chemicals to form a mild solution of sulfuric acid and nitric acid.
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9	Measuring Acid Rain Acid rain is measured using a "pH" scale. The lower a substance's pH, the more acidic it is. Pure water has a pH of 7.0. Normal rain is slightly acidic and has a pH of about 5.5. As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3.
10	Effects of Acid Rain The strength of the effects depend on many factors How acidic the water is The chemistry and buffering capacity of the soils involved The types of fish, trees, and other living things that rely on the water
11	Effects of Acid Rain Has a variety of effects, including damage to forests and soils, fish and other living things, materials, and human health. Also reduces how far and how clearly we can see through the air, an effect called visibility reduction.
12	Effects of Acid Rain Effects of acid rain are most clearly seen in the aquatic environments Most lakes and streams have a pH between 6 and 8
13	Buffering Capacity Acid rain primarily affects sensitive bodies of water, which are located in watersheds whose soils have a limited "buffering capacity“ Lakes and streams become acidic when the water itself and its surrounding soil cannot buffer the acid rain enough to neutralize it.
14	"In areas where buffering capacity..." In areas where buffering capacity is low, acid rain also releases aluminum from soils into lakes and streams; aluminum is highly toxic to many species of aquatic organisms.
15	Effects on Wildlife Generally, the young of most species are more sensitive to environmental conditions than adults. At pH 5, most fish eggs cannot hatch. At lower pH levels, some adult fish die. Some acid lakes have no fish.
16	Effects on Wildlife Both low pH and increased aluminum levels are directly toxic to fish. In addition, low pH and increased aluminum levels cause chronic stress that may not kill individual fish, but leads to lower body weight and smaller size and makes fish less able to compete for food and habitat.
17	Acid Rain and Forests Acid rain does not usually kill trees directly. Instead, it is more likely to weaken trees by damaging their leaves, limiting the nutrients available to them, or exposing them to toxic substances slowly released from the soil.
18	Nutrients Acidic water dissolves the nutrients and helpful minerals in the soil and then washes them away before trees and other plants can use them to grow. Acid rain also causes the release of substances that are toxic to trees and plants, such as aluminum, into the soil.
19	Reducing Acid Rain EPA's Acid Rain Program limits, or "caps," sulfur dioxide (SO₂) emissions from power plants at 8.95 million tons annually, allows those plants to trade SO₂ allowances, and reduces nitrogen oxide emission rates.
20	Global Warming Energy from the sun drives the earth’s weather and climate, and heats the earth’s surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat.
21	Greenhouse Effect Without this natural “greenhouse effect,” temperatures would be much lower than they are now Problems may arise when the atmospheric concentration of greenhouse gases increases.
22	Greenhouse Gases Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide (CO) have increased nearly 30%, methane (CH₄) concentrations have more than doubled, and nitrous oxide (NO_x)concentrations have risen by about 15%.
23	Fossil Fuels The combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide.
24	Changing Climate Global mean surface temperatures have increased 0.5-1.0°F since the late 19th century. The 20th century's 10 warmest years all occurred in the last 15 years of the century. Of these, 1998 was the warmest year on record.
25	Effects of Global Warming The snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean have decreased. Globally, sea level has risen 4-8 inches over the past century.
26	Effects of Global Warming Worldwide precipitation over land has increased by about one percent. The frequency of extreme rainfall events has increased throughout much of the United States.
27	Future Changes Scientists expect that the average global surface temperature could rise 1-4.5°F (0.6-2.5°C) in the next fifty years, and 2.2-10°F (1.4-5.8°C) in the next century, with significant regional variation.
28	Future Changes Evaporation will increase as the climate warms, which will increase average global precipitation. Soil moisture is likely to decline in many regions, and intense rainstorms are likely to become more frequent. Sea level is likely to rise two feet along most of the U.S. coast.